The present invention relates to a method of manufacturing a semiconductor device havng an ion-implanted layer.
A conventional n-channel MOS transistor is manufactured in a manner as shown in FIGS. 1A to 3.
Silicon nitride film 3 is formed on p-type silicon substrate 1 through silicon oxide buffer film 2. First resist pattern 7 is formed on oxide film 2, using first mask 6 obtained by forming chromium film 5 at a predetermined portion of the surface of glass plate 4 and having a central opening. Then, using resist pattern 7 and silicon nitride film 3 as a mask, boron, e.g., is ion-implanted into substrate 1, thereby forming ion-implanted layer 8 (shown in FIGS. 1A and 1B). After pattern 7 is removed, annealing is performed, using film 3 as a mask, forming field oxide film 9. Boron in layer 8 is activated, forming first impurity layer 10 of P.sup.+ -type (which has higher impurity concentration than that of the P-type substrate). Film 3 and underlying film 2 are then removed, and second resist pattern 12 is formed, using second mask 11 (a frame-like mask having a central opening). Boron ions are then reimplanted into substrate 1, using resist pattern 12 as a mask, thus forming p.sup.+ -type second impurity layer 13 (shown in FIGS. 2A and 2B). Note that leakage current between source and drain regions decreases due to layer 13. After pattern 12 is removed, gate oxide film 14 and polycrystalline silicon gate electrode 15 are sequentially formed on a substrate region (SDG portion) surrounded by film 9. Phosphorus ions are implanted into substrate 1, using electrode 15 as a mask, forming n.sup.+ -type source and drain regions 16 and 17. As a result, an n-channel MOS transistor (shown in FIG. 3).
According to the conventional technique, however, pattern 7 for forming layer 8, and pattern 12 for forming layer 13 are formed separately. Hence, different types of mask must be used for first and second masks 6 and 11. These decreases the efficiency of manufacture and increases the manufacturing costs.